Various micro-cavity resonators have been utilized to re-circulate light and store optical power. In a typical micro-cavity resonator, light traverses around an interior surface of the cavity. The optical power stored in the resonator can be used in cavity quantum electrodynamics (cQED), photonics, and various other optics applications as well as sensing applications.
For example, known micro-cavities include surface tension induced micro-cavities (STIM), such as droplets or micro-spheres. The surface quality or finish of a resonator usually affects how long light can re-circulate in the resonator. For example, STIM micro-spheres, which typically have smooth surfaces, allow light energy to be stored for relatively long periods of time and provide a high Q factor or Q value. The Q factor is known as 1/Q=1/Q(scat)+1/Q(mat), where Q(scat) approximates surface scattering and Q(mat) approximates material loss. The Q factor measures the stability of light within a resonator. In other words, the Q value measures the relationship between stored energy and the rate of dissipation of the energy. The Q factors of microspheres are typically greater than 100 million or 10.sup.8.
Other known micro-resonators, such as toroid-shaped resonators, have been able to achieve Q factors similar to Q factors of these STIM spherical resonators, but are also planar devices. The advantage of a planar device is the ease of integration with existing optical and electrical circuitry as well as device fabrication protocols using typical processing techniques.
While micro-cavity resonators having various Q values may be integrated with various devices, some applications and systems can be used with resonators having Q values that are lower than Q values achieved with, for example, micro-spheres. Further, some applications and systems may be cost sensitive and require less expensive micro-resonators.
Resonator devices have been produced using different fabrication techniques and materials depending on required Q capabilities and associated costs. For example, polymer resonator devices have been made using a conventional molding process that uses a master silicon disk. A molding material is applied to the silicon disk to form a mold cavity. The mold cavity is filled with a polymer, which is cured to form a polymer resonator.
However, these conventional molding processes involving a silicon disk have a number of shortcomings. The mold prepared from the silicon disk is not sufficiently smooth due to the surface irregularities of the master silicon disk. The roughness is initiated during the photolithography, which creates the initial shape of the disk and multiplied during the etching process which forms the disk. These surface irregularities are transferred to the mold which, in turn, are transferred to the polymer disc resonators that are made from the mold.
These surface irregularities can have serious negative effects on polymer resonator performance. For example, while polymer resonators prepared with molding processes using a silicon master have achieved maximum Q factors of about 105, their theoretical Q factor based upon the absorption of the material is well above 107. For example, the highest known Q factor of known polymer-based devices is 1.3×105, as discussed in P. Rabiei, W. Steier, C. Zhang, L. Dalton, J Lightwave Tech 20 11 2002. This disparity between the achieved Q factor and the theoretical one is a result of the surface roughness, which leads to surface scattering and degradation of Q. The Q factor achieved, 105, is orders of magnitude less than Q factors of other known silica spherical and microtoroid micro-resonators. Accordingly, the uses for conventional “low-Q” polymer resonators and molding processes are quite limited.
Further, conventional molding processes do not allow for molding of polymer resonators having various shapes, such as overhanging features. Rather, known disk molding processes are typically limited to cylindrical disk shapes or rings, as previously discussed. Additionally, possible polymer materials that can be used in known molding processes are limited, thereby limiting the resulting polymer resonators and related applications. Further, the polymer molding and replica materials used in conventional processes may not be sufficiently flexible, thereby impacting the integrity of the replica resonators since the mold and/or the resonator materials may be too stiff or rigid and more prone to damage. These shortcomings are particularly acute when attempting to apply conventional molding processes to resonators having “non-disk” shapes, such as toroid resonators having overhanging and other pronounced structures. Conventional molding processes cannot effectively prepare a mold of an overhanging structure or a replica polymer resonator having such a structure.
Accordingly, there exists a need for a micro-molding process that can effectively prepare polymer resonators with useful Q factors and for a replica polymer resonator that has surface qualities that support these Q factors. The process should be able to prepare molds and replica polymer resonators with smooth surfaces that support improved Q factors, such as smooth spherical and toroid surfaces. The molding process should also be utilized with various shapes and sizes of resonators, including resonators having overhanging or other pronounced structures. The process should also be non-destructive so that the master can be utilized after the molding process. It is also desirable to repeat the molding process with the same mold to produce additional replica polymer resonators. The process and resulting polymer resonators should also be time and cost efficient, and reliable. The molded resonators should also have a useful shelf life.